Re: Watchpoint prorogation to child threads

[Mark Wielaard <mark@klomp.org>]

Hi Phil,

On Tue, 2008-02-26 at 16:11 +0000, Phil Muldoon wrote:
> Mark Wielaard wrote:
> > It would be nice if this is similar to the breakpoints. Low-level
> > breakpoints are the same on a clone (because they are really just
> > markers in the code segment which is the same), but they are cleared on
> > exec (because then the memory of the process is reset). 
> 
> I'm not sure I understand, are breakpoints propagated on clone or not? I 
> think they should, and I think I agree on the similarity.

Yes, the low-level breakpoints are propagated (by virtue of them being
actually inside the code segment that are shared between clones). But
higher-level Code observers still work per Task, so on that level you
need to register a new Code observer for a new Task to get notified when
they trigger (they still trigger of course, but if nobody is
listening...). I assume a Watch is similar to a Code, both being
TaskObservers (and the comments look funnily similar).

> To be honest, not thought about the exec issue, but yeah  I guess the 
> memory is reset.

The memory is, and for low-level breakpoints we reset the internal data
structures for that reason on an exec event. Since you are implementing
low-level watchpoints with hardware support in the cpu register you
might have to also clear those (if the kernel doesn't do that for you on
an exec).

Cheers,

Mark